1. Field of the Invention
The present invention relates to a hydraulic shock absorber for a vehicle.
2. Description of the Related Art
A conventional hydraulic shock absorber includes a damper cylinder provided in inner portions of an outer tube and an inner tube, and a piston is slidably in contact with an inner periphery of the damper cylinder. As described in Japanese Examined Patent Publication (JP-B) No. 63-23957, to simplify the structure and reduce the number of parts, there is provided a structure in which a piston is slidably in contact with an inner periphery of the inner tube without the damper cylinder.
The conventional hydraulic shock absorber is structured to: slidably insert an inner tube within an outer tube via bushes which are respectively fixed to an opening portion in an inner periphery of the outer tube and a front end portion in an outer periphery of the inner tube; section an annular oil chamber which is surrounded by the inner periphery of the outer tube, the outer periphery of the inner tube and the two bushes; provide with a partition member in an inner periphery of the inner tube so as to section an oil chamber in a lower portion, slidably insert a piston rod which is mounted to the outer tube to the partition member; fix a piston which is slidably in contact with the inner periphery of the inner tube to a front end portion of the piston rod which is inserted to the inner tube so as to section the oil chamber into a piston rod side oil chamber in which the piston rod is received and a piston side oil chamber in which the piston rod is not received, and; communicate the annular oil chamber with the piston rod side oil chamber via an oil hole which is provided in the inner tube.
In this structure, a cross sectional area of the annular oil chamber is set to be substantially equal to a cross sectional area of the piston rod. A volume compensation chamber which is formed by an elastic tube body absorbing a volume expansion of a working fluid is provided in the oil chamber in an inner portion of the inner tube.
Accordingly, the working fluid which corresponds to a move-into volumetric capacity of the piston rod moving into the inner tube in a compression stroke is transferred to the annular oil chamber from the oil chamber in the inner periphery of the inner tube via the oil hole of the inner tube. Further, the working fluid which corresponds to a move-out volumetric capacity of the piston rod moving out from the inner tube in an expansion stroke is transferred to the oil chamber in the inner periphery of the inner tube from the annular oil chamber via the oil hole of the inner tube. Further, a volumetric capacity expansion due to a temperature increase of the oil is compensated by the volume compensation chamber which is provided in the inner portion of the inner tube.
In the conventional art, since the structure is made such that the cross sectional area of the annular oil chamber is set to be substantially equal to the cross sectional area of the piston rod, the following problems are generated.
(1) It is very delicate to set the outer diameter of the piston rod and the annular gap between the outer tube and the inner tube, and a pressure condition in the inner portion of the inner tube changes according to differences in size due to a tolerance in the working size.
(2) In the case of using the piston rod having a constant outer diameter, it is necessary to make the annular gap narrow as the inner tube has the larger diameter, resulting in a limitation in design.
(3) In the case that the annular gap is fixed, it is necessary to make the outer diameter of the piston rod larger as the inner tube has the larger diameter, with the result that it is impossible to make the parts of the piston rod common.
An object of the present invention is to provide a hydraulic shock absorber in which a piston is slidably in contact with an inner periphery of an inner tube, wherein no delicate operation is required for setting an annular gap between an outer tube and an inner tube.
According to the present invention, there is disclosed a hydraulic shock absorber for a vehicle which is structured as follows.
An inner tube is slidably insertable within an outer tube via bushes which are respectively fixed to an opening portion in an inner periphery of the outer tube and a front end portion in an outer periphery of the inner tube.
An annular oil chamber which is surrounded by the inner periphery of the outer tube, the outer periphery of the inner tube and the two bushes is sectioned.
A partition member is disposed in an inner periphery of the inner tube so as to section an oil chamber in a lower portion and section an air chamber in an upper portion.
A piston rod which is mounted to the outer tube is slidably insertable to the partition member.
A piston which is slidably in contact with the inner periphery of the inner tube is fixable to a front end portion of the piston rod which is inserted to the inner tubes, so as to section the oil chamber into a piston rod side oil chamber in which the piston rod is received and a piston side oil chamber in which the piston rod is not received.
An annular oil chamber is communicatable with the piston rod side oil chamber or the piston side oil chamber via an oil hole which is provided in the inner tube.
A cross sectional area of the annular oil chamber is formed larger than a cross sectional area of the piston rod. A check valve which inhibits a flow from the oil chamber into the oil storage chamber at a time of an expansion side stroke is provided in the partition member. A micro flow passage which passes through the oil chamber and the oil storage chamber is provided in the partition member.